﻿namespace Hx.ADSyncPlatform.Infrastructure.Expression
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;

    namespace Common
    {
        public static class ExpressionFuncExtenstion
        {
            /// <summary>
            ///     以特定的条件运行组合两个Expression表达式
            /// </summary>
            /// <typeparam name="T">表达式的主实体类型</typeparam>
            /// <param name="first">第一个Expression表达式</param>
            /// <param name="second">要组合的Expression表达式</param>
            /// <param name="merge">组合条件运算方式</param>
            /// <returns>组合后的表达式</returns>
            public static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second,
                Func<Expression, Expression, Expression> merge)
            {
                var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
                var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
                return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
            }

            /// <summary>
            ///     以 Expression.AndAlso 组合两个Expression表达式
            /// </summary>
            /// <typeparam name="T">表达式的主实体类型</typeparam>
            /// <param name="first">第一个Expression表达式</param>
            /// <param name="second">要组合的Expression表达式</param>
            /// <returns>组合后的表达式</returns>
            public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first,
                Expression<Func<T, bool>> second)
            {
                return first.Compose(second, Expression.AndAlso);
            }

            /// <summary>
            ///     以 Expression.OrElse 组合两个Expression表达式
            /// </summary>
            /// <typeparam name="T">表达式的主实体类型</typeparam>
            /// <param name="first">第一个Expression表达式</param>
            /// <param name="second">要组合的Expression表达式</param>
            /// <returns>组合后的表达式</returns>
            public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first,
                Expression<Func<T, bool>> second)
            {
                return first.Compose(second, Expression.OrElse);
            }

            private class ParameterRebinder : ExpressionVisitor
            {
                private readonly Dictionary<ParameterExpression, ParameterExpression> _map;

                private ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
                {
                    _map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
                }

                public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map,
                    Expression exp)
                {
                    return new ParameterRebinder(map).Visit(exp);
                }

                protected override Expression VisitParameter(ParameterExpression node)
                {
                    ParameterExpression replacement;
                    if (_map.TryGetValue(node, out replacement))
                        node = replacement;
                    return base.VisitParameter(node);
                }
            }
        }
    }
}
